There is a desire in the industry for higher circuit density in microelectronic devices which are made using lithographic techniques. One method of achieving higher circuit density is to improve the resolution of the lithographic patterns made in the photoresist film.
Radiation backscattering during exposure caused by reflections from the topographical features of the substrate are a significant contribution to linewidth variation and resolution problems.
One technique for improving the resolution of lithographic patterns in photoresist involves forming multilayered resists. A thick polymer layer is first coated on the substrate over the surface topography to provide a planar surface upon which a thin photosensitive imaging resist layer is uniformly coated. When the photosensitive layer is imagewise exposed to radiation, the thick polymer layer absorbs radiation before it strikes the substrate. After the imaging layer is imagewise exposed to radiation and developed, it is used as an etch mask to delineate the planarizing layer. The image is then transferred from the imaging layer through the planarizing layer to the substrate.
However, in many cases, when the top photosensitive layer of the resist is spun onto the planarizing layer, the organic solvent causes interfacial mixing of the two layers. In order to prevent interfacial mixing, it is standard practice to crosslink the bottom layer. For example, crosslinked novolac is a common bottom layer for multilayer resists. However, the crosslinking of the bottom planarizing layer inhibits the subsequent stripping of the resist.
It is therefore the object of the present invention to provide an improved multilayer photoresist film.
The other objects and advantages will become apparent from the following disclosure.